Life's geological origins vis a vis panspermia

[headscratcher]

In the question of how life appeared on Earth, did it arrive or emerge, the geology of the Earth is important. Geologic elements needed for life must have concentrated to be useful. The material of Earth arrived in a mixed hodge podge of dust, molton and vaporized minerals from meteors, proto planets and comets impacting, heating, melting, vaporizing and spreading their matter all over. Life appears in the fossil record almost as soon as water. Computer simulations show liquid water could have appeared even before the end of the late heavy bombardment. The water was however ephermeral. The solid rock that appeared and could hold water protected from the hot molton primordial surface would be subsumed into the lava and the water would again be vaporized. Most of the surface was molton but cooling and solidifying, melting and solidifying again. Eventualy the surface stabilized, at least in some places, for water, life and the evidence of water and life to be preserved until today. We don't know if the evidence we have might have formed even when much of the surface was still molton sometime during the late heavy bombardment.

The surface was composed of widely and thinly spread minerals mixed into impermiable basalt and dust. Minerals are concentrated in water by water passing through permiable rock and dust, dissolving the minerals and depositing them in concentrates. There are many way for this to happen. Some minerals dissolve in water and deposit in concentration easily some don't. Some require complex preexisting concentrations of minerals to dissolve in water and complex concentrations of other minerals to deposit in concentration.

In order for life to survive on Earth certain minerals must have concentrated and moved into some degree of complexity of mixed concentrations with other minerals. Some were moved into mixture by water and some were moved by geologic drift forces. This takes time. More so the more complex the mixture of minerals.

Clearly the mixture of minerals in water was complex enough shortly after water appeared for life to have survived. However we know life can survive in mixtures of mineral concentrates of relatively low complexity. For life to emerge we believe a much higher complexity of minerals would be required.

Conclusion

Life could have survived on Earth in the mixture of mineral concentrates available had it arrived from elsewhere before we believe it could have emerged sponaneously from minerals available on Earth.

[bystander]

All Life on Earth Could Have Come From Alien Zombies
Wired Science | 10 Nov 2010

'Necropanspermia' suggested as a way of seeding life on Earth
PhysOrg | Space Exploration | 11 Nov 2010

Astronomy Without A Telescope – Necropanspermia
Universe Today | 13 Nov 2010

Panspermia, Past and Present: Astrophysical and Biophysical Conditions for the Dissemination of Life in Space - Paul S. Wesson

• Space Science Review (14 July 2010) DOI: 10.1007/s11214-010-9671-x
  arXiv.org > astro-ph > arXiv:1011.0101 > 30 Oct 2010

[Chris Peterson]

Life could have survived on Earth in the mixture of mineral concentrates available had it arrived from elsewhere before we believe it could have emerged sponaneously from minerals available on Earth.

I don't believe the science of abiogenesis has advanced far enough to say when life might have emerged from what was available on the Earth. It isn't even known to what degree the surface of the Earth was modified by external material. And based on observational evidence, it isn't yet at all clear when the first life actually did occur- there's quite a bit of disagreement about what was present for around a billion years before the first unambiguous fossil evidence. Life may well have developed deep in the crust, or deep under oceans, when surface conditions were extremely hostile to any life, homegrown or external.

[bystander]

Did Life First Come To This Earth In A Meteor
Sunday Magazine | 19 Nov 2010

[i][size=120][b]DID LIFE FIRST COME TO THIS EARTH IN A METEOR:[/b][/size] Arrhenius, Following Kelvin, Holds That Its Initial Germs Were Brought Here in a Fragment of an Exploded World, and That Particles of Our Globe Are Now Taking Life to Others.[/i] New York Times Sunday Magazine 20 Nov 1910 ([url=http://www.sundaymagazine.org/wp-content/uploads/19101120-1-did.pdf]PDF[/url])

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Before we go into the details of this article, take another look at the photo of the meteorite above and make sure you see the children. I missed them the first time. That meteorite is known as the Willamette Meteorite and it can still be seen in the Hayden Planetarium* at the American Museum of Natural History, where it has been since 1906.

In the article, astronomer Mary Proctor (whose articles for the Times Magazine have graced this site before) discusses panspermia, the idea that life can spread throughout the universe carried on meteors and asteroids.

The first time I heard about panspermia, my mind was blown. I hadn’t considered that life could have come here from somewhere else. But it makes sense as a possibility. And if meteors can theoretically bring life to our planet, that means we can theoretically send life to other planets. Wait a minute! What if those first crafts we sent to Mars weren’t completely sterile? What if we sent a germ, bacteria, or other microbe capable of withstanding space travel and Mars’ atmosphere? Perhaps over the next hundred million years it could evolve into something more intelligent than us!

[jaksichj]

I have seen arguments for and against panspermia in a different forum--of which I participate---and I tend to agree with Chris Peterson on the advances --or lack thereof-- in determining lifes' origins to many details. However, the latest findings and my personal studies tend to indicate that life may have had some "encouragement" --if you will--- from comets / and -or / meteorites; as well as, the position of our planet at the time of "seeding". Of late there has been in the literature --authoritative studies by individuals from NASA-Huntsville AL, Univ of Calif-San Diego, Harvard, Columbia Univ, and the Herzberg Institute in Canada--the studies seem to lend credence to one possible scenario in particular:



(1) There seems to be a favoritism to left-handed chirality among life bearing molecules on earth -- and among bio-important molecules distributed among collected meteorites
(2) So-called "seeding" of the planet was best achieved when the planet was rather hot ---during a period of time where the earth was possibly less than 500 Million yrs old
(3) The temperature of the earth played a significant role in life's origin on the planet--a case in point---the controversial incident of red rain in India--micro-organisms within rain---itself point to an ultra-extremo-phile that is said to be stable up to temperatures of 600 K---it is postulated that the first life did not utilize oxygen for respiration.
(4) Work by Dr. Richard Hoover from the NASA--Huntsville, Al site has been progressing on work to sort through life's origins--and presented some of his ongoing work at the SPIES---meeting in 2010 San Diego-his conclusion from the studiy of meteorite fragments i.e. Murchison meteorite --just one which he studied via Scanning Microscope reveal "definite" evidence for micro-organism --not of possible earth origin
(5) Further work by Dr. Hoover and work performed at Columbia Univ. by Dr. Ronald Breslow, indedpendently--indicate that there is a preference for left-handed chirality --


I am not trying to come-off like some crack-pot--I can readily give the references --if anyone needs them.

It is in MHO--this planet is currently (and was in the past) in a "Very Sweet" zone

[bactame]

Life on Earth is going to disappear in the future, that is a concrete fact. A discussion about when it appeared seems rather trite and it has disappeared from the scientific publications i am familiar with at least 20 years ago. If this were 1930 and Tombaugh were around we would be reading such things, but it isn't. The water, all of it in liquid forms, will be gone in 1-2 billion years so, long before the sun blinks out and we will have done so as well. Finding bacteria on distant planets is a sign that other life can exist there as well and i don't think sending meteors to those places is very significant to our means of doing some of the research ourselves. We have a good long time available to our future and it might be good to work on this future.

Knowing where men came from is pretty well a consensus these days, knowing where bacteria came from is quite beside the point.

[Chris Peterson]

Life on Earth is going to disappear in the future, that is a concrete fact. A discussion about when it appeared seems rather trite and it has disappeared from the scientific publications i am familiar with at least 20 years ago.

The abiogenic origins of life on Earth (and by extension, elsewhere) is a pretty hot area of research, and there are many papers currently published on the subject every year. The theories that have been proposed are interesting and very testable.

[bystander]

More Asteroids Could Have Made Life’s Ingredients
Universe Today | Nancy Atkinson | 2011 Jan 18
Source: NASA GSFC Press Release

This artist's concept uses hands to illustrate the left and right-handed versions of the amino acid isovaline. [i](Credit: NASA/Mary Pat Hrybyk-Keith)[/i]

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This is a photo of a carbon-rich meteorite analyzed in the study. [i](Credit: Antarctic Meteorite Laboratory/NASA Johnson Space Center)[/i]

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A wider range of asteroids were capable of creating the kind of amino acids used by life on Earth, according to new NASA research. Amino acids are used to build proteins, which are used by life to make structures like hair and nails, and to speed up or regulate chemical reactions. Amino acids come in two varieties that are mirror images of each other, like your hands. Life on Earth uses the left-handed kind exclusively. Since life based on right-handed amino acids would presumably work fine, scientists are trying to find out why Earth-based life favored left-handed amino acids.

In March, 2009, researchers at NASA’s Goddard Space Flight Center in Greenbelt, Md., reported the discovery of an excess of the left-handed form of the amino acid isovaline in samples of meteorites that came from carbon-rich asteroids. This suggests that perhaps left-handed life got its start in space, where conditions in asteroids favored the creation of left-handed amino acids. Meteorite impacts could have supplied this material, enriched in left-handed molecules, to Earth. The bias toward left-handedness would have been perpetuated as this material was incorporated into emerging life.

In the new research, the team reports finding excess left-handed isovaline (L-isovaline) in a much wider variety of carbon-rich meteorites. “This tells us our initial discovery wasn’t a fluke; that there really was something going on in the asteroids where these meteorites came from that favors the creation of left-handed amino acids,” says Dr. Daniel Glavin of NASA Goddard. Glavin is lead author of a paper about this research published online in Meteoritics and Planetary Science January 17.

“This research builds on over a decade of work on excesses of left-handed isovaline in carbon-rich meteorites,” said Dr. Jason Dworkin of NASA Goddard, a co-author on the paper.

“Initially, John Cronin and Sandra Pizzarello of Arizona State University showed a small but significant excess of L-isovaline in two CM2 meteorites. Last year we showed that L-isovaline excesses appear to track with the history of hot water on the asteroid from which the meteorites came. In this work we have studied some exceptionally rare meteorites which witnessed large amounts of water on the asteroid. We were gratified that the meteorites in this study corroborate our hypothesis,” explained Dworkin.

L-isovaline excesses in these additional water-altered type 1 meteorites (i.e. CM1 and CR1) suggest that extra left-handed amino acids in water-altered meteorites are much more common than previously thought, according to Glavin. Now the question is what process creates extra left-handed amino acids. There are several options, and it will take more research to identify the specific reaction, according to the team.

However, “liquid water seems to be the key,” notes Glavin. “We can tell how much these asteroids were altered by liquid water by analyzing the minerals their meteorites contain. The more these asteroids were altered, the greater the excess L-isovaline we found. This indicates some process involving liquid water favors the creation of left-handed amino acids.”

Another clue comes from the total amount of isovaline found in each meteorite. “In the meteorites with the largest left-handed excess, we find about 1,000 times less isovaline than in meteorites with a small or non-detectable left-handed excess. This tells us that to get the excess, you need to use up or destroy the amino acid, so the process is a double-edged sword,” says Glavin.

Whatever it may be, the water-alteration process only amplifies a small existing left-handed excess, it does not create the bias, according to Glavin. Something in the pre-solar nebula (a vast cloud of gas and dust from which our solar system, and probably many others, were born) created a small initial bias toward L-isovaline and presumably many other left-handed amino acids as well.

One possibility is radiation. Space is filled with objects like massive stars, neutron stars, and black holes, just to name a few, that produce many kinds of radiation. It’s possible that the radiation encountered by our solar system in its youth made left-handed amino acids slightly more likely to be created, or right-handed amino acids a bit more likely to be destroyed, according to Glavin.

It’s also possible that other young solar systems encountered different radiation that favored right-handed amino acids. If life emerged in one of these solar systems, perhaps the bias toward right-handed amino acids would be built in just as it may have been for left-handed amino acids here, according to Glavin.

[bystander]

Meteorite holds clues to organic chemistry of the early Earth
Carnegie Institute of Science | 2011 Jun 09

Carbonaceous chondrites are a type of organic-rich meteorite that contain samples of the materials that took part in the creation of our planets nearly 4.6 billion years ago, including materials that were likely formed before our Solar System was created and may have been crucial to the formation of life on Earth. The complex suite of organic materials found in carbonaceous chondrites can vary substantially from meteorite to meteorite. New research from Carnegie's Department of Terrestrial Magnetism and Geophysical Laboratory, published June 10 in Science, shows that most of these variations are the result of hydrothermal activity that took place within a few million years of the formation of the Solar System, when the meteorites were still part of larger parent bodies, likely asteroids.

Organic material in carbonaceous chondrites shares many characteristics with organic matter found in other primitive samples, including interplanetary dust particles, comet 81P/Wild-2, and Antarctic micrometeorites. It has been argued by some that this similarity indicates that organic material throughout the Solar System largely originated from a common source, possibly the interstellar medium.

A test of this common-source hypothesis stems from its requirement that the organic diversity within and among meteorites be due primarily to chemical and thermal processing that took place while the meteorites were parts of their parent bodies. In other words, there should be a relationship between the extent of hydrothermal alteration that a meteorite experienced and the chemistry of the organic material it contains.

If--as many have speculated--the organic material in meteorites had a role to play in the origin of life on Earth, the attraction of the common-source hypothesis is that the same organic material would have been delivered to all bodies in the Solar System. If the common source was the interstellar medium, then similar material would also be delivered to any forming planetary system.

The research team—led by Christopher Herd of the University of Alberta, Canada, and including Carnegie's Conel Alexander, Larry Nittler, Frank Gyngard, George Cody, Marilyn Fogel, and Yoko Kebukawa—studied four meteorite specimens from the shower of stones, produced by the breakup of a meteoroid as it entered the atmosphere, that fell on Tagish Lake in northern Canada in January 2000. The samples are considered very pristine, because they fell on a frozen lake, were collected without hand contact within a few days of landing and have remained frozen ever since.

The samples were processed and analyzed on the microscopic level using a variety of sophisticated techniques. Examination of their inorganic components indicated that the specimens had experienced large differences in the extent of hydrothermal alteration, prompting an in-depth examination of their organic material. The team demonstrated that the insoluble organic matter found in the samples has properties that span nearly the entire range found in all carbonaceous chondrites and that those properties correlate with other measures of the extent of parent body alteration. Their finding confirms that the diversity of this material is due to processing of a common precursor material in the asteroidal parent bodies.

The team found large concentrations of monocarboxylic acids, or MCAs, which are essential to biochemistry, in their Tagish Lake samples. They attributed the high level of these acids to the pristine nature of the samples, which have been preserved below zero degrees Celsius since they were recovered. There was variety in the types of MCAs, which they determined could also be due to alterations that took place on the parent bodies.

The samples also contained amino acids—the essential-for-life organic building blocks used to create proteins. The types and abundances of amino acids contained in the samples are consistent with an extraterrestrial origin, and were clearly also influenced, albeit in a complex way, by the alteration histories of their host meteorites.

"Taken together these results indicate that the chemical and thermal processing common to the Tagish Lake meteorites likely occurred when the samples were part of a larger parent body that was created from the same raw materials that formed our Solar System," said Larry Nittler of Carnegie's DTM. "These samples can also provide important clues to the source of organic material, and life, on Earth."

The stuff of life hitched ride to Earth on asteroid
University of Alberta | 2011 Jun 10

Detailed analysis of the most pristine meteorite ever recovered shows that the composition of the organic compounds it carried changed during the early years of the solar system. Those changed organics were preserved through billions of years in outer space before the meteorite crashed to Earth.

The research team, led by University of Alberta geologist Chris Herd, analyzed samples of a meteorite that landed on Tagish Lake in northern British Columbia in 2000. Variations in the geology of the meteorite samples were visible to the naked eye and indicated the asteroid, from which the meteorite samples originated, had gone through substantial changes.

The researchers began looking for variations in the organic chemistry that corresponded with variations in the meteorite's geology. Herd says they found a surprising correlation, which gave researchers a snapshot of the process that altered the composition of organic material carried by the asteroid. Among the organic compounds studied were amino acids and monocarboxylic acids, two chemicals essential to the evolution of the first, simple life forms on Earth.

Herd says the finding shows the importance of asteroids to Earth's history. “The mix of prebiotic molecules, so essential to jump-starting life, depended on what was happening out there in the asteroid belt,” said Herd. “The geology of an asteroid has an influence on what molecules actually make to the surface of Earth.”

Herd says that, when the asteroid was created by the accumulation of dust around the infant sun, it contained ice. The ice warmed and turned to water, which began percolating and altering the organic compounds buried in the rock.

The Tagish Lake meteorite is considered to be one-of-a-kind because of its landing and handling. It was January when the meteorite exploded at an altitude of 30 to 50 kilometres above Earth and rained meteorite fragments down on the frozen, snow-covered lake. The individual who recovered the samples consulted with experts beforehand and avoided any contamination issues.

Herd says the meteorite's pristine state enabled the breakthrough research. “The variations in the organic makeup are true to what was happing inside the asteroid,” said Herd. “This is exactly what has been orbiting in the asteroid belt for the last 4.5 billion years.”

The research will be published June 9 in the journal Science.

Asteroid Served Up "Custom Orders" of Life's Ingredients
NASA GSFC | 2011 Jun 09

Some asteroids may have been like "molecular factories" cranking out life's ingredients and shipping them to Earth via meteorite impacts, according to scientists who've made discoveries of molecules essential for life in material from certain kinds of asteroids and comets. Now it appears that at least one may have been less like a rigid assembly line and more like a flexible diner that doesn't mind making changes to the menu.

In January, 2000, a large meteoroid exploded in the atmosphere over northern British Columbia, Canada, and rained fragments across the frozen surface of Tagish Lake. Because many people witnessed the fireball, pieces were collected within days and kept preserved in their frozen state. This ensured that there was very little contamination from terrestrial life.

"The Tagish Lake meteorite fell on a frozen lake in the middle of winter and was collected in a way to make it the best preserved meteorite in the world," said Dr. Christopher Herd of the University of Alberta, Edmonton, Canada, lead author of a paper about the analysis of the meteorite fragments published June 10 in the journal Science.

"The first Tagish Lake samples -- the ones we used in our study that were collected within days of the fall -- are the closest we have to an asteroid sample return mission in terms of cleanliness," adds Dr. Michael Callahan of NASA's Goddard Space Flight Center in Greenbelt, Md., a co-author on the paper.

The Tagish Lake meteorites are rich in carbon and, like other meteorites of this type, the team discovered the fragments contained an assortment of organic matter including amino acids, which are the building blocks of proteins. Proteins are used by life to build structures like hair and nails, and to speed up or regulate chemical reactions. What's new is that the team found different pieces had greatly differing amounts of amino acids.

"We see that some pieces have 10 to 100 times the amount of specific amino acids than other pieces," said Dr. Daniel Glavin of NASA Goddard, also a co-author on the Science paper. "We've never seen this kind of variability from a single parent asteroid before. Only one other meteorite fall, called Almahata Sitta, matches Tagish Lake in terms of diversity, but it came from an asteroid that appears to be a mash-up of many different asteroids."

By identifying the different minerals present in each fragment, the team was able to see how much each had been altered by water. They found that various fragments had been exposed to different amounts of water, and suggest that water alteration may account for the diversity in amino acid production.

"Our research provides new insights into the role that water plays in the modification of pre-biotic molecules on asteroids," said Herd. "Our results provide perhaps the first clear evidence that water percolating through the asteroid parent body caused some molecules to be formed and others destroyed. The Tagish Lake meteorite provides a unique window into what was happening to organic molecules on asteroids four-and-a-half billion years ago, and the pre-biotic chemistry involved."

If the variability in Tagish Lake turns out to be common, it shows researchers have to be careful in deciding whether meteorites delivered enough bio-molecules to help jump-start life, according to the team.

"Biochemical reactions are concentration dependent," says Callahan. "If you're below the limit, you're toast, but if you're above it, you're OK. One meteorite might have levels below the limit, but the diversity in Tagish Lake shows that collecting just one fragment might not be enough to get the whole story."

Although the meteorites were the most pristine ever recovered, there is still some chance of contamination though contact with the air and surface. However, in one fragment, the amino acid abundances were high enough to show they were made in space by analyzing their isotopes.

Isotopes are versions of an element with different masses; for example, carbon 13 is a heavier, and less common, variety of carbon. Since the chemistry of life prefers lighter isotopes, amino acids enriched in the heavier carbon 13 were likely created in space.

"We found that the amino acids in a fragment of Tagish Lake were enriched in carbon 13, indicating they were probably created by non-biological processes in the parent asteroid," said Dr. Jamie Elsila of NASA Goddard, a co-author on the paper who performed the isotopic analysis.

The team consulted researchers at the Goddard Astrobiology Analytical Lab for their expertise with the difficult analysis. "We specialize in extraterrestrial amino acid and organic matter analysis," said Dr. Jason Dworkin, a co-author on the paper who leads the Goddard laboratory. "We have top-flight, extremely sensitive equipment and the meticulous techniques necessary to make such precise measurements. We plan to refine our techniques with additional challenging assignments so we can apply them to the OSIRIS-REx asteroid sample return mission."

Origin and Evolution of Prebiotic Organic Matter As Inferred from the Tagish Lake Meteorite - CDK Herd et al

• Science 332(6035) 1304 (10 Jun 2011) DOI: 10.1126/science.1203290

[neufer]

Tagish Lake meteorite 2000

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Tagish Lake sighting 2010

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[bystander]

DNA Building Blocks Can Be Made in Space
NASA GSFC | Bill Steigerwald | 2011 Aug 08

[i]Meteorites contain a large variety of nucleobases, an essential building block of DNA. (Artist concept credit: NASA's Goddard Space Flight Center/Chris Smith)[/i]

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NASA-funded researchers have evidence that some building blocks of DNA, the molecule that carries the genetic instructions for life, found in meteorites were likely created in space. The research gives support to the theory that a "kit" of ready-made parts created in space and delivered to Earth by meteorite and comet impacts assisted the origin of life.

"People have been discovering components of DNA in meteorites since the 1960's, but researchers were unsure whether they were really created in space or if instead they came from contamination by terrestrial life," Meteorites contain a large variety of nucleobases, an essential building block of DNA. (Artist concept credit: NASA's Goddard Space Flight Center/Chris Smith)said Dr. Michael Callahan of NASA's Goddard Space Flight Center, Greenbelt, Md. "For the first time, we have three lines of evidence that together give us confidence these DNA building blocks actually were created in space." Callahan is lead author of a paper on the discovery appearing in Proceedings of the National Academy of Sciences of the United States of America.

The discovery adds to a growing body of evidence that the chemistry inside asteroids and comets is capable of making building blocks of essential biological molecules. For example, previously, these scientists at the Goddard Astrobiology Analytical Laboratory have found amino acids in samples of comet Wild 2 from NASA’s Stardust mission, and in various carbon-rich meteorites. Amino acids are used to make proteins, the workhorse molecules of life, used in everything from structures like hair to enzymes, the catalysts that speed up or regulate chemical reactions.

In the new work, the Goddard team ground up samples of twelve carbon-rich meteorites, nine of which were recovered from Antarctica. They extracted each sample with a solution of formic acid and ran them through a liquid chromatograph, an instrument that separates a mixture of compounds. They further analyzed the samples with a mass spectrometer, which helps determine the chemical structure of compounds.

The team found adenine and guanine, which are components of DNA called nucleobases, as well as hypoxanthine and xanthine. DNA resembles a spiral ladder; adenine and guanine connect with two other nucleobases to form the rungs of the ladder. They are part of the code that tells the cellular machinery which proteins to make. Hypoxanthine and xanthine are not found in DNA, but are used in other biological processes.

Also, in two of the meteorites, the team discovered for the first time trace amounts of three molecules related to nucleobases: purine, 2,6-diaminopurine, and 6,8-diaminopurine; the latter two almost never used in biology. These compounds have the same core molecule as nucleobases but with a structure added or removed.

It's these nucleobase-related molecules, called nucleobase analogs, which provide the first piece of evidence that the compounds in the meteorites came from space and not terrestrial contamination. "You would not expect to see these nucleobase analogs if contamination from terrestrial life was the source, because they're not used in biology, aside from one report of 2,6-diaminopurine occurring in a virus (cyanophage S-2L)," said Callahan. "However, if asteroids are behaving like chemical 'factories' cranking out prebiotic material, you would expect them to produce many variants of nucleobases, not just the biological ones, due to the wide variety of ingredients and conditions in each asteroid."

The second piece of evidence involved research to further rule out the possibility of terrestrial contamination as a source of these molecules. The team also analyzed an eight-kilogram (21.4-pound) sample of ice from Antarctica, where most of the meteorites in the study were found, with the same methods used on the meteorites. The amounts of the two nucleobases, plus hypoxanthine and xanthine, found in the ice were much lower -- parts per trillion -- than in the meteorites, where they were generally present at several parts per billion. More significantly, none of the nucleobase analogs were detected in the ice sample. One of the meteorites with nucleobase analog molecules fell in Australia, and the team also analyzed a soil sample collected near the fall site. As with the ice sample, the soil sample had none of the nucleobase analog molecules present in the meteorite.

Thirdly, the team found these nucleobases -- both the biological and non-biological ones -- were produced in a completely non-biological reaction. "In the lab, an identical suite of nucleobases and nucleobase analogs were generated in non-biological chemical reactions containing hydrogen cyanide, ammonia, and water. This provides a plausible mechanism for their synthesis in the asteroid parent bodies, and supports the notion that they are extraterrestrial," says Callahan.

"In fact, there seems to be a 'goldilocks' class of meteorite, the so-called CM2 meteorites, where conditions are just right to make more of these molecules," adds Callahan.

Meteorites: Tool kits for creating life on Earth
Carnegie Institution for Science | 2011 Aug 08

Click to play embedded YouTube video.

NASA-funded researchers have evidence that some building blocks of DNA, the
molecule that carries the genetic instructions for life, found in meteorites were
likely created in space. The research gives support to the theory that a "kit" of
ready-made parts created in space and delivered to Earth by meteorite and comet
impacts assisted the origin of life. (Credit: NASA's Goddard Space Flight Center)

Meteorites hold a record of the chemicals that existed in the early Solar System and that may have been a crucial source of the organic compounds that gave rise to life on Earth. Since the 1960s, scientists have been trying to find proof that nucleobases, the building blocks of our genetic material, came to Earth on meteorites. New research, published next week in the Proceedings of the National Academy of Sciences, indicates that certain nucleobases do reach the Earth from extraterrestrial sources, by way of certain meteorites, and in greater diversity and quantity than previously thought.

Extensive research has shown that amino acids, which string together to form proteins, exist in space and have arrived on our planet piggybacked on a type of organic-rich meteorite called carbonaceous chondrites. But it has been difficult to similarly prove that the nucleobases found on meteorite samples are not due to contamination from sources on Earth.

The research team, which included Jim Cleaves of Carnegie’s Geophysical Laboratory, used advanced spectroscopy techniques to purify and analyze samples from 11 different carbonaceous chondrites and one ureilite, a very rare type of meteorite with a different type of chemical composition. This was the first time all but two of these meteorites had been examined for nucleobases.

Two of the carbonaceous chondrites contained a diverse array of nucleobases and compounds that are structurally similar, so-called nucleobase analogs. Especially telling was the fact that three of these nucleobase analogs are very rare in terrestrial biology. What’s more, significant concentrations of these nucleobases were not found in soil and ice samples from the areas near where the meteorites were collected.

“Finding nucleobase compounds not typically found in Earth’s biochemistry strongly supports an extraterrestrial origin,” Cleaves said.

The team tested their conclusion with experiments to reproduce nucleobases and analogs using chemical reactions of ammonia and cyanide, which are common in space. Their lab-synthesized nucleobases were very similar to those found in the carbonaceous chondrites, although the relative abundances were different. This could be due to chemical and thermal processing that the meteorite-origin nucleobases underwent while traveling through space.

These results have far-reaching implications. The earliest forms of life on Earth may have been assembled from materials delivered to Earth by meteorites.

“This shows us that meteorites may have been molecular tool kits, which provided the essential building blocks for life on Earth,” Cleaves said.

Building Blocks of DNA Found in Meteorites from Space
Space.com | Charles Q Choi | 2011 Aug 08

The components of DNA have now been confirmed to exist in extraterrestrial meteorites, researchers announced.

A different team of scientists also discovered a number of molecules linked with a vital ancient biological process, adding weight to the idea that the earliest forms of life on Earth may have been made up in part from materials delivered to Earth the planet by from space.

Past research had revealed a range of building blocks of life in meteorites, such as the amino acids that make up proteins. Space rocks just like these may have been a vital source of the organic compounds that gave rise to life on Earth.

Investigators have also found nucleobases, key ingredients of DNA, in meteorites before. However, it has been very difficult to prove that these molecules are not contamination from sources on Earth. [5 Bold Claims of Alien Life]

"People have been finding nucleobases in meteorites for about 50 years now, and have been trying to figure out if they are of biological origin or not," study co-author Jim Cleaves, a chemist at the Carnegie Institution of Washington, told SPACE.com.

To help confirm if any nucleobases seen in meteorites were of extraterrestrial origin, scientists used the latest scientific analysis techniques on samples from a dozen meteorites — 11 organic-rich meteorites called carbonaceous chondrites and one ureilite, a very rare type of meteorite with a different chemical composition. This was the first time all but two of these meteorites had been analyzed for nucleobases.

The analytical techniques probed the mass and other features of the molecules to identify the presence of extraterrestrial nucleobases and see that they apparently did not come from the surrounding area.

Two of the carbonaceous chondrites contained a diverse array of nucleobases and structurally similar compounds known as nucleobase analogs. Intriguingly, three of these nucleobase analogs are very rare in Earth biology, and were not found in soil and ice samples from the areas near where the meteorites were collected at the parts-per-billion limits of their detection techniques.

"Finding nucleobase compounds not typically found in Earth's biochemistry strongly supports an extraterrestrial origin," Cleaves said.

"At the start of this project, it looked like the nucleobases in these meteorites were terrestrial contamination — these results were a very big surprise for me," study lead author Michael Callahan, an analytical chemist and astrobiologist at NASA Goddard Space Flight Center, told SPACE.com.

Lab experiments showed that chemical reactions of ammonia and cyanide, compounds that are common in space, could generate nucleobases and nucleobase analogs very similar to those found in the carbonaceous chondrites. However, the relative abundances of these molecules between the experiments and the meteorites differed, which might be due to further chemical and thermal influences from space.

This findings reveal that meteorites may have been molecular tool kits, providing the essential building blocks for life on Earth, Cleaves said. [7 Theories on the Origin of Life]

"All this has implications for the origins of life on Earth and potentially elsewhere," Callahan said. "Are these building blocks of life transferred to other places where they might be useful? Can alternative building blocks be used to build other things?"

In a different study, researchers discovered molecules that make up key parts of a vital biological pathway, the citric acid cycle, in a number of carbonaceous chondrites.

The citric acid cycle is "thought by many experts to be among the most ancient of biological processes," study co-author George Cooper, a chemist at NASA Ames Research Center, told SPACE.com. "One function of this cycle is respiration, when organisms give off carbon dioxide."

"It is always exciting to find extraterrestrial and ancient 4.6 billion-year-old organic compounds that might have had a role in early life," Cooper added.

Cleaves, Cooper and their colleagues detailed their findings in two studies online Aug. 8 in the Proceedings of the National Academy of Sciences.

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